Stripline directional coupler having bent coupling arms

ABSTRACT

A coupled line type directional coupler comprises a first directional coupling unit including mutually insulated first and second metal strip lines having a length of lambda /4 which are crossed three-dimensionally at the center of the directional coupling unit and run parallel to each other, the first and second metal strip lines being bent substantially at a right angle and substantially at the center of the first directional coupling unit; and a second directional coupling unit including mutually insulated third and fourth metal strip lines having a length of lambda /4 which are crossed three-dimensionally at the center of the directional coupling unit and run parallel to each other, the third and fourth strip lines being bent substantially at the center of the second directional coupling unit, whereby the first and second directional coupling units are directly coupled in tandem.

United States Patent [191 Ishii et al.

[451 Sept. 9, 1975 STRIPLINE DIRECTIONAL COUPLER HAVING BENT COUPLINGARMS Inventors: Takimi Ishii, Yokohama; Isao Suzuki, Kawasaki; ToraoNagai, Yokohama, all of Japan Assignee: Tokyo Shibaura Electric Co.,Ltd.,

Kawasaki, Japan Filed: Jan. 31, 1974 App]. No.: 438,404

Primary ExaminerPaul L. Gensler Attorney, Agent, or FirmOblon, Fisher,Spivak, McClelland & Maier [5 7] ABSTRACT A coupled line typedirectional coupler comprises a first directional coupling unitincluding mutually insulated first and second metal strip lines having alength of M4 which are crossed three-dimensionally at the center of thedirectional coupling unit and run parallel to each other, the first andsecond metal strip lines being bent substantially at a right angle andsubstantially at the center of the first directional coupling unit; anda second directional coupling unit including mutually insulated thirdand fourth metal strip lines having a length of M4 which are crossedthreedimensionally at the center of the directional coupling unit andrun parallel to each other, the third and fourth strip lines being bentsubstantially at the center of the second directional coupling unit,whereby the first and second directional coupling units are directlycoupled in tandem.

2 Claims, 5 Drawing Figures [30] Foreign Application Priority Data Feb.12, 1973 Japan 48-17212 [52] US. Cl. 333/10; 333/84 M [51] Int. Cl.I-lOlp 5/14 [58] Field of Search 333/10, 84 M [56] References CitedUNITED STATES PATENTS 3,167,727 1/1965 Lunden et al 333/l0 X 3,737,8106/1973 Shelton 333/10 PORTI L PORT lll PATENTED 91975 3.904.991.

F I G. 1 PRIOR ART PORT 1 Y A PORT I11 PORT 11 1 1 PORT 1v PORT 1 v 1PORT 111 F l G. 2

PORT H Y APORT EZ -FIG.3

3o PORTHI 1 PoFmV PATEHTED SEP 9 75 SHEET 2 BF 2 FIG. 4

PORT 1V PORT 111 FREQUENCY (GHZ 1 STRIPLINE DIRECTIONAL COUPLER HAVINGBENT COUPLING ARMS This invention relates to a coupled line typedirectional coupler, particularly to a directional coupler for use in amicrowave strip circuit.

A coupled line type directional coupler as shown in FIG. 1 has been usedas a mixer in amicrowave receiving device. The coupled line typedirectional coupler is provided with directional coupling units 1, 2coupled in tandem. The directional coupling unit I has a pair of striplines 3, 4 having a length of M4 (A being the wavelength of the handledsignal) which are crossed at the center of the directional coupling unitand run parallel to each other. The directional coupling units 1, 2 arecoupled in tandem by means of strip lines 7, 8.

With the directional coupler, the strip lines 7, 8 are advantageouslymade longer so as to prevent a mutual influence of the directionalcoupling units 1, 2. However, when the strip lines 7, 8 are made longer,the strip lines 7, 8 per se impart an influence to the characteristicsof the coupled line type directional coupler. Furthermore, a bulkierdirectional coupler results. Therefore, the length of the strip lines 7,8 is empirically determined to be M4. FIG. 4 shows in broken linesoutput characteristics at a port II and VSWR at a port I involved when asignal of 2.0-4.0 GHz is applied to the port I. As will be evident fromthis figure, an amount of attenuation of an output at the port II isbelow 20 dB and VSWR is l.3l .4 which indicates a poor characteristic.

This invention relates to a small-sized directional coupler whosecharacteristics are improved.

In one aspect of this invention there is provided a directional couplingcomprising a first directional coupling unit having mutually insulatedfirst and second strip lines having a length of M4 which are crossed atone location and run parallel to each other, the first and second striplines being bent, a second directional coupling unit having mutuallyinsulated third and fourth strip lines having a length of M4 which arecrossed at one location and run parallel to each other, the third andfourth strip lines being bent, whereby the first and second directionalcoupling units are directly coupled in tandem.

This invention can be more fully understood from the following detaileddescription when taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a diagrammatic view showing a conventional coupled line typedirectional coupler;

F IG. 2 is a diagrammatic view illustrating the principle of a coupledline type directional coupler according to this invention;

FIG. 3 is a perspective view of a directional coupler based on theprinciple of FIG. 2;

FIG. 4 is an explanatory view showing the characteristics of coupledline type directional couplers based on the principle of FIGS. 1 and 2;and

FIG. 5 is a diagrammatic view illustrating the principle of anothercoupled line type directional coupler according to this invention.

A coupled line type directional coupler shown in FIG. 2 is provided withdirectional coupling units ll, 12 having a degree of coupling of 8.34dB. The directional coupling unit 1] has mutually insulated metal striplines 13, 14 having a length of M4 which are threedimensionally crossedsubstantially at the central portion of the directional coupling unitand run parallel to each other at the remaining portion. The directionalcoupling unit 12 has mutually insulated metal strip lines 15, 16 havinga length of N4 which are threedimensionally crossed substantially at thecentral portion of the directional coupling unit 12 and run parallel toeach other at the remaining portion. The metal strip lines 13, 14 andl5, 16 are bent substantially at a right angle at the crossed centralportion so that the respective both ends of the metal strip lines l3, 14are arranged opposite to the respective both ends of the metal striplines 15, 16. One end of the metal strip line 13 is coupled directly toone end of the metal strip line 16 which is opposite to the one end ofthe strip line 13 and one end of the metal strip line 14 correspondingto the other end of the strip line 13 is coupled directly to one end ofthe metal strip line 15 corresponding to the other end of the strip line16 so that the directional coupling units 11 and 12 are coupled intandem to provide a directional coupler. The respective other ends ofthe metal strip lines 13, l4, l5 and 16 are extended to form ports I,II, III and IV. The metal strip lines 14 and 16 have metal strips 17 and18, respectively. The metal strip 17 spans the metal strip 13 at onelocation where the metal strip lines 13 and 14 are to be crossedrelative to each other, while the metal strip 18 spans the metal strip15 at one location where the metal strip lines 15 and 16 are to becrossed relative to each other.

The directional coupler has no coupling strip lines 7, 8 for thedirectional coupler shown in FIG. 1. This completely obviatesdisadvantages such as the bulkiness of a directional coupler,deterioration of directivity and VSWR, and so on. caused due to thepresence of such coupling strip lines.

FIG. 3 shows one embodiment based on the principle of FIG. 2. Adirectional coupler of the type shown in FIG. 2 is formed on an aluminasubstrate 21. Sections corresponding to respective metal strips l3, l4,l5, 16 are formed on an alumina substrate 21 (dielectric constant 10.5)of a chromiumgold double layer having a 0.635 mm thickness. Gold strips17 and 18 are used to span the strip lines 13 and 15, respectively. Thewidth of each strip line is made to be 0.380 mm and a spacing betweenthe strip lines 13 and 14 and a spacing between the strip lines 15 and16 are made to be 0.110 mm, respectively. Respective ports I, II, III,IV are connected to coaxial plugs 22, 23, 24, 25 so as to be coupled toouter coaxial lines (not shown). The substrate 21 is secured to a metalblock 30 by fitting means 26, 27, 28 and 29. In a graphicalrepresentation of FIG. 4 solid lines show output characteristics at theports II, III and IV and VSWR at the port I involved when input signalis applied to the port I of the coupled line type directional coupler.An operating central frequency is 3 GHZ. As will be evident from thisfigure, an amount of attenuation at the outlet of the port II isimproved up to more than 20 dB and VSWR is restricted to below 1.2.

Such improved characteristics are attained by directly coupling thedirectional coupling units 11 and 12 in tandem without interposing anystrip lines such as coupling strip lines 7, 8 etc. as is found in aconventional direction coupler. Furthermore, it is possible to reducethe size of a directional coupler to a greater extent by bending thedirectional coupling unit as shown in FIG. 2.

With the above-mentioned embodiment the direc tional coupling units 11,12 are bent at a right angle substantially at the center thereof.However, the directional coupling unit may be bent at an acute or obtuseangle. The directional coupling unit may be coupled in a semicircularshape as shown in FIG. 5. The metal strip lines l3, l4 and l5, 16 arecrossed substantially at the respective center thereof. However, thecrossed portions may be located at other than the center of the striplines. Though with the above-mentioned embodiment two directionalcoupling units are coupled in tandem, a plurality of directionalcoupling units may be coupled in tandem.

What is claimed is:

l. A directional coupler comprising a first directional coupling unitincluding mutually insulated first and second strip lines having alength of )\/4 where A is the wavelength of the handled signal which arecrossed at one portion and run parallel to each other at the remainingportion, the first and second strips being bent, a second directionalcoupling unit including mutually insulated third and fourth strip lineshaving a length of M4 which are crossed at one portion and run parallelto each other at the other portion, the third and fourth strip linesbeing bent so that the respective both ends of the first and secondstrip lines are opposite to the respective both ends of the third andfourth strip lines,

the first and second directional coupling units being directly coupledin tandem, the first and second lines being bent substantially at aright angle and crossed at the center thereof and the third and fourthstrip lines being bent substantially at a right angle and crossed at thecenter thereof.

2. A directional coupler comprising a first directional coupling unitincluding mutually insulated first and second strip lines having alength of M4 where A is the wavelength of the handled signal which arecrossed at one portion and run parallel to each other at the remainingportion, the first and second strips being bent, a second directionalcoupling unit including mutually insulated third and fourth strip lineshaving a length of M4 which are crossed at one portion and run parallelto each other at the other portion, the third and fourth strip linesbeing bent so that the respective both ends of the first and secondstrip lines are opposite to the respective both ends of the third andfourth strip lines, the first and second directional coupling unitsbeing directly coupled in tandem, the first and second strip lines beingbent in a semi-circular shape and crossed at the center thereof and thethird and fourth strip lines being bent in a semi-circular shape andcrossed at the

1. A directional coupler comprising a first directional coupling unitincluding mutually insulated first and second strip lines having alength of lambda /4 where lambda is the wavelength of the handled signalwhich are crossed at one portion and run parallel to each other at theremaining portion, the first and second strips being bent, a seconddirectional coupling unit including mutually insulated third and fourthstrip lines having a length of lambda /4 which are crossed at oneportion and run parallel to each other at the other portion, the thirdand fourth strip lines being bent so that the respective both ends ofthe first and second strip lines are opposite to the respective bothends of the third and fourth strip lines, the first and seconddirectional coupling units being directly coupled in tandem, the firstand second lines being bent substantially at a right angle and crossedat the center thereof and the third and fourth strip lines being bentsubstantially at a right angle and crossed at the center thereof.
 2. Adirectional coupler comprising a first directional coupling unitincluding mutually insulated first and second strip lines having alength of lambda /4 where lambda is the wavelength of the handled signalwhich are crossed at one portion and run parallel to each other at theremaining portion, the first and second strips being bent, a seconddirectional coupling unit including mutually insulated third and fourthstrip lines having a length of lambda /4 which are crossed at oneportion and run parallel to each other at the other portion, the thirdand fourth strip lines being bent so that the respective both ends ofthe first and second strip lines are opposite to the respective bothends of the third and fourth strip lines, the first and seconddirectional coupling units being directly coupled in tandem, the firstand second strip lines being bent in a semi-circular shape and crossedat the center thereof and the third and fourth strip lines being bent ina semi-circular shape and crossed at the center thereof.